722  Standardisation  of  Digitalis  Preparations.  {AN0vemberPhia9™" 
may  give  rise  to  inaccurate  results,  especially  when  dealing  with 
tinctures  of  which  the  history  and  origin  are  unknown. 
Some  investigators  claim  to  have  standardized  digitalis  prepara- 
tions by  the  use  of  "  pithed  "  frogs  and  the  Williams  Apparatus,  in- 
jecting the  drug  and  noting  (i)  the  time  taken  to  kill  the  heart,  and 
(2)  the  number  of  heart  beats;  calculating  their  results  from  stand- 
ard tinctures  of  digitalis  or  from  solutions  of  strophanthin.  From 
my  own  tests  I  have  not  found  this  method  reliable. 
M.L.D.  methods  by  injection  show  toxicity  only  and  not  thera- 
peutic value. 
Perfusion  Experiments. 
The  apparatus  used  was  in  some  respects  similar  to  that  de- 
scribed in  my  first  paper  (P.  Dec,  191 5).  I  found  it  necessary  to 
modify  it  very  considerably. 
The  glass  reservoir  A  contains  Ringer's  normal  saline  solution. 
B  contains  a  solution  of  the  tincture  to  be  tested  1  per  cent,  in 
Ringer's  solution. 
The  reservoirs  were  fitted  with  internal  tubes  as  before  (to  keep 
the  pressure  constant).  The  stand  which  carried  these  was  grad- 
uated on  the  upright,  the  zero  mark  being  placed  in  such  a  position 
that  the  level  of  the  lower  ends  of  the  air-tubes  A  and  B  were  the 
same  height  from  the  table  as  the  end  of  the  canula  C.  The  pressure 
is  thus  regulated  by  raising  or  lowering  the  cross-arm  S.  The  Y 
tube,  mentioned  before,  was  substituted  by  a  combination  of  three 
3-way  taps,  which  I  found  much  more  convenient  than  clips.  The 
frog  was  "  pithed "  and  dissected  as  before,  a  glass  canula  being 
inserted  into  the  inferior  vena  cava  and  carefully  ligatured,  care 
being  taken  that  no  leakage  was  possible  at  the  joint — the  two  aortse 
were  left  intact  in  this  experiment  and  the  solutions  perfused 
through  the  body  to  the  other  cut  end  of  the  inferior  vena  cava, 
which  was  left  open,  thus  allowing  the  perfused  solutions  to  escape 
from  the  body,  through  the  perforated  frog  plate,  into  the  tray  T, 
and  thence  to  the  outlet  "  N,"  which  is  a  glass  tube  of  y%  in.  bore. 
The  drops  of  Hqui4  from  here  operate  the  small  trigger  "K,"  which 
was  counterbalanced  and  connected  up  with  the  writing  lever  "  R  " ; 
thus  each  drop  was  registered  on  the  tracing. 
"  S,"  the  heart  lever,  is  connected  to  the  heart  as  before. 
"  F,"  the  time  marker,  registers  every  five  seconds. 
The  apparatus  was  arranged  so  that  the  height  of  the  air-tubes 
